D15 swap to D15Bv-tec

I am wondering how hard it will to swap these motors. I am swapping in a 93 Honda Civic Hatchback. I was told that it would increase my gas mileage by swapping engines. I was also told that putting a cold air intake would also help my gas mileage. Will changing the exhaust increase horsepower and possibly gas mileage? I am looking for a little more power. Right now I just want gas mileage.

The best mods for gas mileage are just bolt on I/H/E setups. You increase the efficiency of the engine without making it more thirsty. Don't bother swapping. A good intake will make a good bit of difference without too much cost. Adding an exhaust and header will help too, but those tend to cost a bit more.